On Wednesday, workers began replacing four-foot-high guardrails with taller concrete barriers along the outside of the elevated stretch of roadway over the Bronx Zoo, as well as two other similarly constructed viaducts.

“It won’t change what happened on Sunday but we feel it will be an additional barrier for traffic safety,” Department of Transportation Commissioner Joan McDonald said.

Crews also began adding signs and striping on the highway.

The state is also considering permanently reducing the speed limit on the roadway.

Bronx Borough President Ruben Diaz Jr. applauded the state’s swift response and said the changes are a “step in the right direction.”

“Whenever you lose three generations of family members in this fashion, we in the government have a responsibility to examine and to see what is it that we could do to ensure that this doesn’t happen again,” Diaz said.

The accident was the second in the past year to involve a car falling off of the same stretch of the Bronx River Parkway. Last June, the driver of a sport utility vehicle heading north, lost control, hit a divider, bounced through two lanes of traffic and fell 20 feet over a guard rail, landing on a pickup truck in a parking lot. The two people in the SUV were injured.

In a 2006 crash, an Acura carrying seven people jumped the median and was crushed by an oncoming bus. That accident resulted in five deaths.